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A validation of short-duration scientific tows as a representation of long commercial-length tows: Comparing the catch rates, size composition and species composition of prawn trawler bycatch in the far northern Great Barrier Reef, Australia

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Wassenberg, T.J., Burridge, C.Y., Connell, M. and Gribble, N. (1998) A validation of short-duration scientific tows as a representation of long commercial-length tows: Comparing the catch rates, size composition and species composition of prawn trawler bycatch in the far northern Great Barrier Reef, Australia. Fisheries Research, 36 (1). pp. 35-46. ISSN 0165-7836

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Article Link: https://doi.org/10.1016/S0165-7836(98)00076-9

Abstract

The duration of tows for scientific trawl surveys in northern Australia is generally 30 min. Commercial trawls may be up to 200 min long. In this study we compare the catch rates, size of fish and species composition for 10 short (30 min) tows paired with 10 commercial length (165 min—not in a straight line) tows at both an inshore and an offshore location in the far northern Great Barrier Reef. Evaluations of this kind have not been reported in tropical Australian multi-species fisheries. Overall, catch rates of fish and invertebrates differed between short and long tows both inshore and offshore. Inshore, the mean catch rate for the fish and the invertebrates was significantly greater in short duration tows (P<0.05). Offshore, the mean catch rate for all fish, and all invertebrates was not significantly different between short and long tows, although higher catch rates of invertebrates were recorded in long tows. Inshore, 12 fish species out of 49 had significantly different catch rates, most being greater in short tows. Only 2 invertebrates out of 16 had significantly different catch rates (P<0.05). The combined weight of species showing significant differences in catch rates represented less than 10% of the total weight in both inshore and offshore samples. Principal component analysis indicated that catch composition was similar between short and long tows both inshore and offshore. The results from our sampling are that the species composition of 30-min trawls is similar to that of commercial length tows, and that size frequencies are equivalent. The implications are that short tows (30 min) can be used in scientific surveys to give a true representation of both size and species composition of commercial length tows, but may overestimate catch rates.

Item Type:Article
Keywords:Catch comparison; Catch rates; Shrimp trawl; Tropical fish sampling
Subjects:Aquaculture and Fisheries > Fisheries > By region or country > Australia > Great Barrier Reef
Aquaculture and Fisheries > Fisheries > Methods and gear. Catching of fish
Aquaculture and Fisheries > Fisheries > Shellfish fisheries
Live Archive:15 Mar 2024 04:53
Last Modified:15 Mar 2024 04:53

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